I'm having a lot of difficulty finding info on the properties of virtual photons - things like their polarization when exchanged between positively and negatively charged particles. Feynman says, in his book QED: the strange thory of light and matter, at p. 120: Photons, it turns out, come in four different varieties, called polarizations, that are related geometrically to the directions of space and time. Thus there are photons polarized in the X, Y, Z, and T directions. (Perhaps you have heard somewhere that light comes in only two states of polarization - for example, a photon going in the Z direction can be polarized at right angles, either in the X or Y direction. Well, you guessed it: in situations where the photon goes a long distance and appears to go at the speed of light, the amplitudes for the Z and T terms exactly cancel out. But for virtual photons going between a proton and an electron in an atom, it is the T component that is the most important.) [emphasis added] Unfortunately, he doesn't elaborate beyond that. Does anyone know of a book, or where I can find info, in simple plain English as above, that describes the properties of virtual photons (such as their polarization) when exchanged between positively and negatively charged particles?